Device and method for multi-link operations

ABSTRACT

Embodiments of a device and a method for multi-link operations are disclosed. In an embodiment, a device includes a processor configured to perform a first backoff operation on a first link and a second backoff operation on a second link of a multi-link device (MLD) that has a non-simultaneous transmission and reception capability (NSTR MLD), and transmit a first Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) on the first link at a first start time after the first backoff operation and a second PPDU on the second link at a second start time after the second backoff operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of U.S. Provisional PatentApplication Ser. No. 63/112,545, filed on Nov. 11, 2020, and U.S.Provisional Patent Application Ser. No. 63/121,507, filed on Dec. 4,2020, each of which is incorporated by reference herein.

BACKGROUND

In multi-link operations, wireless devices, e.g., multi-link devices(MLDs), can execute various wireless operations, such as coordinate somefeatures or operations for devices in a multi-link operation via one ormore links. As an example, a wireless device may transmit frames on alink after a backoff counter becomes zero. However, because somewireless devices may simultaneously transmit frames on multiple links,backoff operations for simultaneous transmissions may also need to bedefined for when multiple backoff counters on a link are zero.

SUMMARY

Embodiments of a device and a method for multi-link operations aredisclosed. In an embodiment, a device includes a processor configured toperform a first backoff operation on a first link and a second backoffoperation on a second link of a multi-link device (MLD) that has anon-simultaneous transmission and reception capability (NSTR MLD), andtransmit a first Physical Layer Convergence Protocol (PLCP) ProtocolData Unit (PPDU) on the first link at a first start time after the firstbackoff operation and a second PPDU on the second link at a second starttime after the second backoff operation.

In an embodiment, a difference between the first start time and thesecond start time is no more than a Receive-Transmit Turnaround Time(aRxTxTurnaroundTime).

In an embodiment, a difference between the first start time and thesecond start time is no more than 4 microseconds (μs).

In an embodiment, a first backoff counter of the first backoff operationbecomes zero after a first backoff counter of the second backoffoperation and a second backoff counter of the second backoff operationhave become zero.

In an embodiment, the first backoff counter of the second backoffoperation and the second backoff counter of the second backoff operationbecome zero at different times.

In an embodiment, the first backoff counter of the second backoffoperation and the second backoff counter of the second backoff operationbecome zero at a same time.

In an embodiment, the first PPDU includes a first Aggregated-MediaAccess Control (MAC) Protocol Data Unit (MPDU) (A-MPDU) with frames froma first Access Category (AC), and the second PPDU includes a secondA-MPDU with frames from a second AC.

In an embodiment, the processor is configured to perform another backoffoperation on the second link for an AC that is not included in thesecond PPDU, and where a Contention Window (CW) of the AC (CW[AC]) and aQuality of Service (QoS) Short Reply Counter (QSRC) of the AC (QSRC[AC])are unchanged.

In an embodiment, the processor is configured to perform another backoffoperation on the second link for an AC that is not included in thesecond PPDU after a QSRC[AC] is increased by one and a CW[AC] isdoubled.

In an embodiment, the CW[AC] is doubled if the CW[AC] is less than a maxCW of the AC (CWmax[AC]).

In an embodiment, the CW[AC] is set to a minimum CW of the AC(CWmin[AC]) if the QSRC[AC] reaches a threshold value.

In an embodiment, a first backoff counter of the first backoff operationbecomes zero after a first backoff counter of the second backoffoperation and a second backoff counter of the second backoff operationhave become zero, and where the first PPDU includes a first A-MPDU withframes from a first AC and the second PPDU includes a second A-MPDU withframes from a second AC.

In an embodiment, the second A-MPDU with frames from the second ACcorresponds to at least one of the first backoff counter of the secondbackoff operation and the second backoff counter of the second backoffoperation.

In an embodiment, the processor is configured to perform another backoffoperation on the second link once a backoff counter on the first linkbecomes zero to break a deadlock that occurs after the first backoffoperation and the second backoff operation.

In an embodiment, the processor is configured to perform another backoffoperation on the second link once the second link becomes idle to breaka deadlock that occurs after the first backoff operation and the secondbackoff operation.

In an embodiment, the first backoff operation includes a backoff counterfor a corresponding AC and the second backoff operation includes anotherbackoff counter for another corresponding AC.

In an embodiment, the device includes a first station (STA), STA1, thatperforms the first backoff operation on the first link, and a secondSTA, STA2, that performs the second backoff operation on the secondlink.

In an embodiment, the processor is configured to operate according to anInstitute of Electrical and Electronics Engineers (IEEE) 802.11becommunication protocol.

A method for multi-link operations is also disclosed. The methodinvolves performing, by an NSTR MLD, a first backoff operation on afirst link and a second backoff operation on a second link, andtransmitting, by the NSTR MLD, a first PPDU on the first link at a firststart time after the first backoff operation and a second PPDU on thesecond link at a second start time after the second backoff operation.

Another method for multi-link operations is also disclosed. The methodinvolves performing, by an NSTR MLD, a first backoff operation on afirst link and a second backoff operation on a second link, whereperforming the first backoff operation and the second backoff operationincludes a first STA, STA1, performing the first backoff operation onthe first link, and a second STA, STA2, performing the second backoffoperation on the second link, and transmitting, by STA1 and STA2, afirst PPDU on the first link at a first start time after the firstbackoff operation and a second PPDU on the second link at a second starttime after the second backoff operation.

Other aspects in accordance with the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrated by way of example of the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a multi-link communications system.

FIG. 2 illustrates an example of a technique that may be used by amulti-link device (MLD) that has a non-simultaneous transmission andreception capability (NSTR MLD) to simultaneously transmit PhysicalLayer Convergence Protocol (PLCP) Protocol Data Units (PPDUs) onmultiple links.

FIG. 3 illustrates another example of a technique that may be used by anNSTR MLD to simultaneously transmit PPDUs on multiple links.

FIG. 4 illustrates another example of a technique that may be used by anNSTR MLD to simultaneously transmit PPDUs on multiple links.

FIG. 5 illustrates another example of a technique that may be used by anNSTR MLD to simultaneously transmit PPDUs on multiple links.

FIG. 6 illustrates an example of a deadlock that occurs on multiplelinks.

FIG. 7 illustrates a flow diagram of a technique for multi-linkoperations in accordance with an embodiment of the invention.

Throughout the description, similar reference numbers may be used toidentify similar elements.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by this detailed description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussions of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or similar language means that a particular feature,structure, or characteristic described in connection with the indicatedembodiment is included in at least one embodiment of the presentinvention. Thus, the phrases “in one embodiment”, “in an embodiment”,and similar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

In embodiments of a multi-link communications system, a wireless device,e.g., a multi-link device (MLD) (e.g., an access point (AP) MLD or anon-AP station (STA) MLD) that has a non-simultaneous transmission andreception capability (NSTR MLD) may exchange data frames, managementframes, or control frames (e.g., data Media Access Control (MAC)Protocol Data Units (MPDUs), management MPDUs, or control MPDUsencapsulated in Physical Layer Convergence Protocol (PLCP) Protocol DataUnits (PPDUs)) with at least one MLD associated with the NSTR MLD. Insome embodiments, frames may correspond to an Access Category (AC), suchthat the AC may be one of four categories: AC Voice (AC_VO), AC Video(AC_VI), AC Best Effort (AC_BE), or AC Background (AC_BK). As describedherein, an “NSTR MLD” may be an AP MLD or a non-AP STA MLD that isunable to simultaneously transmit and receive frames on multiple links,e.g., an NSTR AP MLD or an NSTR non-AP STA MLD. In addition, the MLDassociated with the NSTR MLD may be an NSTR MLD or an MLD that has asimultaneous transmission and reception capability (STR MLD). Asdescribed herein, an “STR MLD” may be an AP MLD or a non-AP STA MLD thatis able to simultaneously transmit and receive frames on multiple links,e.g., an STR AP MLD or an STR non-AP STA MLD. Furthermore, as describedherein, “simultaneous” and/or “simultaneously” may be defined asoccurring concurrently, as occurring in no more than a Receive-TransmitTurnaround Time (aRxTxTurnaroundTime), or as occurring in no more than 4microseconds (μs).

In an embodiment, an MLD (e.g., an NSTR MLD) may include two or moreaccess points (APs) or non-AP stations (STAs) on links associated withthe MLD. As described herein, non-AP STAs (e.g., STAs) of an NSTR MLDmay alternatively be APs. In addition, as described herein, APs of anMLD may alternatively be non-AP STAs (e.g., STAs). As an example, an APor a non-AP STA of an MLD (e.g., NSTR MLD) may have one associated link.In addition, the associated link may have a dedicated radio or share aradio with other link(s), such that a radio may switch to a link forframe exchanges on the link.

An NSTR MLD may be configured to operate with associated MLDs accordingto a communication protocol. For example, the communication protocol maybe an Extremely High Throughput (EHT) communication protocol, or anInstitute of Electrical and Electronics Engineers (IEEE) 802.11becommunication protocol. Features of wireless communications andmulti-link communications systems operating in accordance with the EHTcommunication protocol and/or next-generation communication protocolsmay be referred to herein as “non-legacy” features. In some embodimentsof the multi-link communications system described herein, differentassociated APs of an MLD (or STAs of an MLD) within range of a STA of anNSTR MLD (or an AP of an NSTR MLD) operating according to the EHTcommunication protocol are configured to operate according to at leastone other communication protocol, which defines operation in a BasicService Set (BSS) with the STA of the NSTR MLD (or the AP of the NSTRMLD), but are generally affiliated with lower data throughput protocols.The lower data throughput communication protocols (e.g., High Efficiency(HE) communication protocol, Very High Throughput (VHT) communicationprotocol, etc.) may be collectively referred to herein as “legacy”communication protocols.

FIG. 1 depicts a multi-link communications system 100 that is used forwireless (e.g., Wi-Fi) communications. In the embodiment depicted inFIG. 1 , the multi-link communications system includes one NSTR MLD(e.g., an NSTR AP MLD or an NSTR non-AP MLD), implemented as NSTR MLD104, and one MLD (e.g., an NSTR AP MLD, an NSTR non-AP MLD, an STR APMLD, or an STR non-AP MLD), implemented as MLD 108. The multi-linkcommunications system can be used in various applications, such asindustrial applications, medical applications, computer applications,and/or consumer or enterprise applications. In some embodiments, themulti-link communications system may be a wireless communicationssystem, such as a wireless communications system compatible with an IEEE802.11 protocol. For example, the multi-link communications system maybe a wireless communications system compatible with the IEEE 802.11beprotocol. Although the depicted multi-link communications system 100 isshown in FIG. 1 with certain components and described with certainfunctionality herein, other embodiments of the multi-link communicationssystem may include fewer or more components to implement the same, less,or more functionality. For example, in some embodiments, the multi-linkcommunications system includes a single NSTR MLD with multiple MLDs, ormultiple NSTR MLDs with more than one MLD. In another example, althoughthe multi-link communications system is shown in FIG. 1 as beingconnected in a certain topology, the network topology of the multi-linkcommunications system is not limited to the topology shown in FIG. 1 .

In the embodiment depicted in FIG. 1 , the NSTR MLD 104 includes twonon-AP STAs, STA1 106-1 and STA2 106-2. In some embodiments, a commonpart of the NSTR MLD 104 implements upper layer MAC functionalities(e.g., beacon creation, MLD association establishment, reordering offrames, etc.) and a link specific part of the NSTR MLD 104, i.e., theSTAs 106-1 and 106-2, implement lower layer MAC functionalities (e.g.,backoff, frame transmission, frame reception, etc.). The STAs 106-1 and106-2 may be implemented in hardware (e.g., circuits), software,firmware, or a combination thereof. The STAs 106-1 and 106-2 may befully or partially implemented as an integrated circuit (IC) device. Insome embodiments, the STAs 106-1 and 106-2 may be compatible with atleast one wireless local area network (WLAN) communications protocol(e.g., at least one IEEE 802.11 protocol). For example, the STAs 106-1and 106-2 may be compatible with the IEEE 802.11be protocol, such thatthe NSTR MLD 104 operates according to the IEEE 802.11be communicationprotocol.

In some embodiments, an NSTR MLD (e.g., NSTR MLD 104) connects to alocal area network (e.g., a LAN) and/or to a backbone network (e.g., theInternet) through a wired connection and wirelessly connects to wirelessAPs (or STAs), for example, through one or more WLAN communicationsprotocols, such as the IEEE 802.11 protocol. In some embodiments, anNSTR radio (e.g., an NSTR radio related to STA1 106-1 and/or STA2 106-2)includes at least one antenna, at least one transceiver operablyconnected to the at least one antenna, and at least one controlleroperably connected to the corresponding transceiver. In someembodiments, the at least one transceiver includes a physical layer(PHY) device. The at least one controller may be configured to controlthe at least one transceiver to process received packets through the atleast one antenna. In some embodiments, the at least one controller maybe implemented in a device that includes a processor, for example, amicrocontroller, a host processor, a host, a digital signal processor(DSP), or a central processing unit (CPU), or a combination thereof,which can be integrated in a corresponding transceiver. In someembodiments, each of the STAs 106-1 or 106-2 of the NSTR MLD 104 mayoperate in a different BSS operating channel. For example, STA1 106-1may operate in a 320 MHz BSS operating channel at 6 GHz band and STA2106-2 may operate in a 160 MHz BSS operating channel at 5 GHz band.Although the NSTR MLD 104 is shown in FIG. 1 as including two STAs,other embodiments of the NSTR MLD 104 may include more than two STAsthat use more than two radios. In addition, although the NSTR MLD 104 isshown in FIG. 1 as including STAs, the STAs may alternatively be APs.

In the embodiment depicted in FIG. 1 , the MLD, implemented as MLD 108,includes two APs, AP1 110-1 and AP2 110-2. The APs 110-1 and 110-2 maybe implemented in hardware (e.g., circuits), software, firmware, or acombination thereof. The APs 110-1 and 110-2 may be fully or partiallyimplemented as an IC device. In some embodiments, the APs 110-1 and110-2 are part of the MLD 108, such that the MLD may be a communicationsdevice that wirelessly connects to a wireless NSTR MLD. For example, theMLD 108 may be implemented in a laptop, a desktop personal computer(PC), a mobile phone, or other communications device that supports atleast one WLAN communications protocol. In some embodiments, the MLD 108is a communications device compatible with at least one IEEE 802.11protocol (e.g., the IEEE 802.11be protocol). In some embodiments, theMLD 108 implements a common MAC data service interface and the APs 110-1and 110-2 implement a lower layer MAC data service interface. Althoughthe MLD 108 is shown in FIG. 1 as including two APs, other embodimentsof the MLD 108 may include one AP or more than two APs that use morethan two radios. In addition, although the MLD 108 is shown in FIG. 1 asincluding APs, the APs may alternatively be STAs.

In some embodiments, the NSTR MLD 104 and/or the MLD 108 can identifywhich communication links support multi-link operation during amulti-link operation setup phase and/or exchange information regardingmulti-link capabilities during the multi-link operation setup phase. Insome embodiments, each of the APs 110-1 and 110-2 of the MLD 108 mayoperate in a different frequency band. For example, AP1 110-1 mayoperate in the 2.4 GHz frequency band and AP2 110-2 may operate in the 5GHz frequency band. In some embodiments, each AP includes at least oneantenna, at least one transceiver operably connected to the at least oneantenna, and at least one controller connected to the correspondingtransceiver. In some embodiments, the at least one transceiver includesa PHY device. The at least one controller may be configured to controlthe at least one transceiver to process received packets through the atleast one antenna. In some embodiments, the at least one controller maybe implemented within a processor, such as a microcontroller, a hostprocessor, a host, a DSP, a CPU, or a combination thereof, which can beintegrated in a corresponding transceiver.

In the embodiment depicted in FIG. 1 , the NSTR MLD 104 communicateswith the MLD 108 via two communication links, e.g., link1 102-1 andlink2 102-2. For example, each of the STAs 106-1 or 106-2 communicateswith APs 110-1 or 110-2 via corresponding communication links 102-1 or102-2. In an embodiment, a communication link (e.g., link1 102-1 orlink2 102-2) may include a BSS operating channel established by a STA ofan NSTR MLD (or an AP of an NSTR MLD) (e.g., STA1 106-1 or STA2 106-2)that features multiple 20 MHz channels used to transmit frames betweenan NSTR MLD and an MLD. In some embodiments, a 20 MHz channel may be apunctured 20 MHz channel or an unpunctured 20 MHz channel. In addition,although the NSTR MLD 104 communicates (e.g., wirelessly communicates)with the MLD 108 via links 102-1 and 102-2, in other embodiments, theNSTR MLD 104 may communicate (e.g., wirelessly communicate) with the MLD108 via more than two communication links.

In some embodiments, an MLD (e.g., an NSTR MLD or an STR MLD) transmitsPPDUs to an associated MLD (e.g., an NSTR MLD or an STR MLD) on multiplelinks (e.g., link1 102-1 and link2 102-2), such that a PPDU transmittedby the MLD to the associated MLD may have a start time and an end time.As described herein, a “start time” may be defined as a time at which anMLD begins to transmit a PPDU, and an “end time” may be defined as atime at which the MLD finishes transmitting the PPDU. In an embodiment,a first PPDU transmitted on a first link has a first start time and afirst end time, and a second PPDU transmitted on a second link has asecond start time and a second end time.

According to conventional wireless communications, the first end time ofthe first PPDU and the second end time of the second PPDU can be thesame or different depending on whether the PPDUs solicit respondingPPDUs. When the PPDUs are addressed to an NSTR MLD and solicitresponding PPDUs, the first end time of the first PPDU and the secondend time of the second PPDU may need to be the same so that the NSTR MLDcan transmit the responding PPDUs simultaneously. For example, if thefirst PPDU and the second PPDU include trigger frames (solicitresponding PPDUs) with a Carrier Sensing (CS) Required subfield set toone, then the first end time cannot be more than aRxTxTurnaroundTime or4 μs earlier than the second end time. When the PPDUs are addressed toan NSTR MLD and do not solicit responding PPDUs, the first end time ofthe first PPDU and the second end time of the second PPDU can be thesame or different. For example, if the first PPDU and the second PPDU donot include trigger frames with the CS Required subfield set to one,then a difference between the first end time and the second end timecannot be more than a Short Interframe Space (SIFS) Time (aSIFSTime)plus a Signal Extension (aSignalExtension) divided by two((aSIFSTime+aSignalExtension)/2) or 8 μs.

In an embodiment, the first start time of the first PPDU and the secondstart time of the second PPDU can be the same or different. As anexample, when an NSTR MLD transmits multiple PPDUs on more than onelink, start times of the PPDUs on different links may need to be thesame. In such an example, the start times of the PPDUs are the same if adifference between the start times is less than a threshold value. Asanother example, an NSTR MLD (e.g., STAs of an NSTR MLD) may eithertransmit one PPDU on one link (e.g., link1 102-1) or transmit multiplePPDUs on multiple links (e.g., link1 102-1 and link2 102-2). The NSTRMLD can transmit one PPDU on one link when a backoff counter of otherlinks is not zero. If the NSTR MLD prefers to transmit PPDUs on multiplelinks, then the PPDUs are transmitted when backoff counters of themultiple links become zero at a same time, or when the backoff counterof one link becomes zero while the backoff counter of another link iszero and a medium (e.g., a channel medium, a link, a band, etc.) isidle. As described herein, a “backoff counter” may feature a slot-basedbackoff counter which counts down from a Contention Window (CW) of an AC(CW[AC]) to zero via values from slot boundaries or time slots, and maycorrespond to an AP or a non-AP STA of an MLD (e.g., NSTR MLD). In suchan example, start times of simultaneously transmitted PPDUs by the NSTRMLD may not need to be exactly the same. However, because the NSTR MLDmay not be able to transmit a PPDU on one link while performing abackoff operation (e.g., Clear Channel Assessment (CCA) sensing) onanother link, a difference between the start times of the PPDUs cannotbe too big.

In conventional backoff operations, a STA of an NSTR MLD (or an AP of anNSTR MLD) may follow channel access procedures when simultaneouslytransmitting PPDUs on multiple links. In one embodiment, a STA of anNSTR MLD (or an AP of an NSTR MLD) may initiate transmission on a linkwhen a medium is idle and either (i) a backoff counter of the STA of theNSTR MLD (or the AP of the NSTR MLD) becomes zero on a slot boundary ofa backoff operation, or (ii) the backoff counter of the STA of the NSTRMLD (or the AP of the NSTR MLD) is already zero and a backoff counter ofanother STA (or AP) associated with the NSTR MLD becomes zero on a slotboundary of a backoff operation. In another embodiment, when a backoffcounter of a STA of an NSTR MLD becomes zero, the STA may choose to nottransmit and to keep the backoff counter at zero. In yet anotherembodiment, if a backoff counter of a STA of an NSTR MLD related to anAC has already become zero, the STA may perform a new backoff operationwhere a CW[AC] and a Quality of Service (QoS) Short Retry Counter (QSRC)of the AC (QSRC[AC]) are unchanged. Thus, although backoff operationsfor simultaneous transmissions on multiple links may be defined, backoffoperations for simultaneous transmissions by an NSTR MLD may also needto be defined for when multiple backoff counters related to multiple ACson a non-AP STA in a link are zero.

In accordance with an embodiment of the invention, a technique formulti-link operations involves performing, by an NSTR MLD, a firstbackoff operation on a first link and a second backoff operation on asecond link, and transmitting, by the NSTR MLD, a first PPDU on thefirst link at a first start time after the first backoff operation and asecond PPDU on the second link at a second start time after the secondbackoff operation. In some embodiments, the technique may be implementedby a communications device (e.g., an NSTR MLD). For example, a devicemay include a processor configured to perform a first backoff operationon a first link and a second backoff operation on a second link of anNSTR MLD, and transmit a first PPDU on the first link at a first starttime after the first backoff operation and a second PPDU on the secondlink at a second start time after the second backoff operation. In anembodiment, a difference between the first start time and the secondstart time is no more than aRxTxTurnaroundTime or 4 μs. By transmittingthe first PPDU and the second PPDU after performing the first backoffoperation and the second backoff operation, such that the differencebetween the first start time and the second start time is no more thanaRxTxTurnaroundTime or 4 μs, multi-link operations may be performed moreefficiently and simultaneous transmissions when multiple backoffcounters on a link are zero may be defined.

Examples of techniques that may be used by an NSTR MLD to simultaneouslytransmit PPDUs on multiple links when multiple backoff counters on alink are zero are described in further detail with reference to FIGS.2-5 .

FIG. 2 illustrates an example of a technique that may be used by an NSTRMLD 204 to simultaneously transmit PPDUs on multiple links. The NSTR MLD204 communicates (e.g., exchanges frames and/or PPDUs) with an MLD,implemented as MLD 208, via two links, link1 202-1 and link2 202-2. Inan embodiment, the NSTR MLD 204 includes two non-AP STAs, STA1 206-1 andSTA2 206-2, and the MLD 208 includes two APs, AP1 210-1 and AP2 210-2.In such an embodiment, STA1 206-1 and AP1 210-1 communicate via link1202-1, and STA2 206-2 and AP2 210-2 communicate via link2 202-2.

STA1 206-1 of the NSTR MLD 204 performs a first backoff operation onlink1 202-1 where a first backoff counter 212-1 of the first backoffoperation corresponds to AC_BE and has a value of ten (shown by tenslots included in the first backoff counter 212-1 on link1 202-1). Afterten slots of idle medium, the backoff counter of AC_BE may become zero(e.g., after a slot with a value of one (shown by a slot that includes“1”)). In addition, STA2 206-2 of the NSTR MLD 204 performs a secondbackoff operation on link2 202-2. The second backoff operation on link2202-2 includes a first backoff counter 212-2 a of the second backoffoperation which corresponds to AC_VO and has a value of four (shown byfour slots included in the first backoff counter 212-2 a on link2202-2), and includes a second backoff counter 212-2 b of the secondbackoff operation which corresponds to AC_BE and has a value of six(shown by six slots included in the second backoff counter 212-2 b onlink2 202-2).

In an embodiment, on link2 202-2, the second backoff counter 212-2 b ofthe second backoff operation becomes zero after the first backoffcounter 212-2 a of the second backoff operation becomes zero, such thatthe first backoff counter 212-2 a of the second backoff operation andthe second backoff counter 212-2 b of the second backoff operationbecome zero at different times. In addition, the first backoff counter212-1 of the first backoff operation becomes zero after the firstbackoff counter 212-2 a of the second backoff operation and the secondbackoff counter 212-2 b of the second backoff operation have becomezero. Although the first backoff counter 212-2 a of the second backoffoperation and the second backoff counter 212-2 b of the second backoffoperation have different values (e.g., end at different slots), thefirst backoff counter 212-2 a and the second backoff counter 212-2 b mayalso have the same value.

After performing the first backoff operation on link1 202-1 and thesecond backoff operation on link2 202-2, the NSTR MLD 204 transmits afirst PPDU 214-1 on link1 202-1 at a first start time 218-1 and a secondPPDU 214-2 on link2 202-2 at a second start time 218-2. A differencebetween the first start time 218-1 and the second start time 218-2 maybe no more than aRxTxTurnaroundTime or 4 μs. In an embodiment, STA2206-2 of the NSTR MLD 204 can select any AC (whose backoff counterbecome zero during a time spent waiting for a backoff counter of STA1206-1 to become zero) as a primary AC, such that STA2 206-2 transmitsframes in a PPDU based on the primary AC selected. For example, thefirst PPDU 214-1 includes a first Aggregated-MPDU (A-MPDU) 216-1 withframes from a first AC (i.e., AC_BE (whose backoff counter is zero) asthe primary AC) and the second PPDU 214-2 includes a second A-MPDU 216-2with frames from a second AC (i.e., AC_BE (whose backoff counter iszero) as the primary AC). In such an embodiment, the second PPDU 214-2also includes padding 220 after the second A-MPDU 216-2 to allow the twoPPDUs, 214-1 and 214-2, to have the same length (if the second A-MPDU216-2 is not enough). Although the second PPDU 214-2 is shown asincluding the second A-MPDU 216-2 with frames from AC_BE, STA2 206-2 canalso select AC_VO as the primary AC so that the second A-MPDU 216-2includes frames from AC_VO.

With reference to FIG. 2 , because the first backoff counter 212-2 a ofthe second backoff operation and the second backoff counter 212-2 b ofthe second backoff operation are zero when the first backoff counter212-1 of the first backoff operation becomes zero, STA2 206-2 can selectany AC whose corresponding backoff counter on link2 202-2 is zero (e.g.,AC_BE or AC_VO) as the primary AC for frame transmission, i.e., thesecond A-MPDU 216-2 included in the second PPDU 214-2 may be from any ACwhose corresponding backoff counter on link2 202-2 is zero (e.g., AC_BEor AC_VO). In an embodiment, a flexible primary AC selection can avoidincluding the padding 220 in the second PPDU 214-2 (not shown). Inanother embodiment, a Transmission Opportunity (TXOP) holder on link2202-2 can select frames from an AC whose TXOP limit is the same as aTXOP limit on link1 202-1.

Although FIG. 2 is shown as including backoff counters and frames whichcorrespond to AC_BE and/or AC_VO, the backoff counters and the framesare not limited to AC_BE and/or AC_VO, and may be AC_VI, AC_BK, or anycombination thereof. In addition, although one backoff counter is shownon link1 202-1 and two backoff counters are shown on link2 202-2, eachlink may include four backoff counters which correspond to the fouraccess categories, e.g., AC_VO, AC_VI, AC_BE, and AC_BK. Furthermore,although the NSTR MLD 204 is described as including STAs and the MLD 208is described as including APs, alternatively, the NSTR MLD 204 mayinclude APs and the MLD 208 may include STAs. In addition, the NSTR MLD204 and the MLD 208 may both be non-AP MLDs.

FIG. 3 illustrates another example of a technique that may be used by anNSTR MLD 304 to simultaneously transmit PPDUs on multiple links. TheNSTR MLD 304 includes STA1 306-1 and STA2 306-2 and communicates vialink1 302-1 and link2 302-2 with an MLD 308 that includes AP1 310-1 andAP2 310-2 as previously described with reference to FIG. 2 . Inaddition, the NSTR MLD 304 transmits a first PPDU 314-1 that includes afirst A-MPDU 316-1 with frames from a first AC as a primary AC (i.e.,AC_BE (whose backoff counter is zero) as the primary AC) on link1 302-1at a first start time 318-1 and a second PPDU 314-2 that includes asecond A-MPDU 316-2 with frames from a second AC as a primary AC (e.g.,AC_VO) and padding 320 on link2 302-2 at a second start time 318-2 afterSTA1 306-1 of the NSTR MLD 304 performs a first backoff operation onlink1 302-1 that includes a first backoff counter 312-1 of the firstbackoff operation, and STA2 306-2 of the NSTR MLD 304 performs a secondbackoff operation on link2 302-2 that includes a first backoff counter312-2 a of the second backoff operation and includes a second backoffcounter 312-2 b of the second backoff operation, similar to thetechnique as previously described with reference to FIG. 2 .

However, as shown in FIG. 3 , the first backoff counter 312-2 a of thesecond backoff operation becomes zero at a same time as the secondbackoff counter 312-2 b of the second backoff operation, such that thefirst backoff counter 312-2 a of the second backoff operation has avalue of six (shown by six slots included in the first backoff counter312-2 a on link2 302-2). In addition, the second A-MPDU 316-2 withframes included in the second PPDU 314-2 corresponds to AC_VO. Thesecond A-MPDU 316-2 with frames included in the second PPDU 314-2corresponds to AC_VO because the technique used by the NSTR MLD 304 tosimultaneously transmit PPDUs on multiple links involves the secondA-MPDU 316-2 with frames corresponding to an AC with highest priority(e.g., AC_VO) and whose backoff counter on link2 302-2 is zero. As anexample, the order of priority for the four access categories fromhighest priority to lowest priority is AC_VO (highest priority), AC_VI,AC_BE, then AC_BK (lowest priority).

FIG. 4 illustrates another example of a technique that may be used by anNSTR MLD 404 to simultaneously transmit PPDUs on multiple links. TheNSTR MLD 404 includes STA1 406-1 and STA2 406-2 and communicates vialink1 402-1 and link2 402-2 with an MLD 408 that includes AP1 410-1 andAP2 410-2 as previously described with reference to FIG. 2 . Inaddition, the NSTR MLD 404 transmits a first PPDU 414-1 that includes afirst A-MPDU 416-1 with frames from a first AC (i.e., AC_BE (whosebackoff counter is zero) as the primary AC) on link1 402-1 at a firststart time 418-1 and a second PPDU 414-2 that includes a second A-MPDU416-2 with frames from a second AC (i.e., AC_BE (whose backoff counteris zero) as the primary AC) on link2 402-2 at a second start time 418-2after STA1 406-1 of the NSTR MLD 404 performs a first backoff operationon link1 402-1 that includes a first backoff counter 412-1 of the firstbackoff operation, and STA2 406-2 of the NSTR MLD 404 performs a secondbackoff operation on link2 402-2 that includes a first backoff counter412-2 a of the second backoff operation and includes a second backoffcounter 412-2 b of the second backoff operation, similar to thetechnique as previously described with reference to FIG. 3 .

In an embodiment, if a STA (e.g., STA2 406-2) has multiple backoffcounters that become zero while deferring its TXOP until a backoffcounter of another link (e.g., backoff counter 412-1 on link1 402-1)becomes zero, then the STA may need to perform a new backoff for an ACwhose frames were not transmitted in the PPDU on the second link (e.g.,the second PPDU 414-2 on link2 402-2). For example, STA2 402-2 mayperform another backoff operation because the second PPDU 414-2 did notinclude frames from AC_VO, such that rules may need to be defined for aCW of AC_VO (CW[AC_VO]) and a QSRC of AC_VO (QSRC[AC_VO]).

In one embodiment, the NSTR MLD 404 may perform another backoffoperation (not shown) on link2 402-2 for an AC (e.g., AC1) whose frameswere not included in the second PPDU 414-2 and whose backoff counterbecame zero at a same time (shown) or at a different time (not shown) asanother AC (e.g., AC2) whose frames were included in the second PPDU414-2, such that a CW of AC1 (CW[AC1]) and a QSRC of AC1 (QSRC[AC1]) areunchanged for AC1, whose frames were not included. For example, becausethe second A-MPDU 416-2 with frames included in the second PPDU 414-2corresponds to AC_BE, the other backoff operation would be for AC_VO,such that the CW[AC_VO] and the QSRC[AC_VO] may be unchanged.

In such an embodiment, if multiple backoff counters of a link (e.g., thefirst backoff counter 412-2 a of the second backoff operation and thesecond backoff counter 412-2 b of the second backoff operation on link2402-2) are zero when a backoff counter of another link (e.g., the firstbackoff counter 412-1 of the first backoff operation on link1 402-1)becomes zero, the backoff counter of link2 402-2 whose frames were notincluded in a PPDU (e.g., the second PPDU 414-2) simultaneouslytransmitted with another PPDU (e.g., the first PPDU 414-1) on link1402-1 performs a new backoff operation where its CW[AC] and QSRC[AC] areunchanged. As an example, the new backoff operation may start at thesecond start time 418-2 where a current CW[AC] and a current QSRC[AC] ofAC_VO (whose frames were not included) are used for the new backoffoperation.

In another embodiment, after a TXOP that includes the transmission ofthe second PPDU 414-2, the NSTR MLD 404 may perform another backoffoperation (not shown) on link2 402-2 for an AC whose frames were notincluded in the second PPDU 414-2 and whose backoff counter became zeroat a same time as another AC whose frames were included in the secondPPDU 414-2, such that a QSRC[AC] is increased by one and a CW[AC] isdoubled if the CW[AC] is less than a CWmax[AC] for the AC whose frameswere not included. For example, because the second A-MPDU 416-2 withframes included in the second PPDU 414-2 corresponds to AC_BE, the otherbackoff operation would be for AC_VO, such that the QSRC[AC_VO] isincreased by one and the CW[AC_VO] is doubled if the CW[AC] is less thana CWmax[AC] for AC_VO.

In such an embodiment, if multiple backoff counters of a link (e.g., thefirst backoff counter 412-2 a of the second backoff operation and thesecond backoff counter 412-2 b of the second backoff operation on link2402-2) are zero when a backoff counter of another link (e.g., the firstbackoff counter 412-1 of the first backoff operation on link1 402-1)becomes zero, the backoff counter of link2 402-2 whose frames were notincluded in a PPDU (e.g., the second PPDU 414-2) simultaneouslytransmitted with another PPDU (e.g., the first PPDU 414-1) on link1402-1 performs a new backoff operation where its QSRC[AC] is increasedby one and CW[AC] is doubled if the CW[AC] is less than a CWmax[AC]. Insome embodiments, the CW[AC] could be set to a CWmin[AC] if the QSRC[AC]that is increased by one reaches a threshold value. As an example, thenew backoff operation may start at the second start time 418-2 after aCW[AC] and a QSRC[AC] of AC_VO is doubled and increased by one,respectively.

FIG. 5 illustrates another example of a technique that may be used by anNSTR MLD 504 to simultaneously transmit PPDUs on multiple links. TheNSTR MLD 504 includes STA1 506-1 and STA2 506-2 and communicates vialink1 502-1 and link2 502-2 with an MLD 508 that includes AP1 510-1 andAP2 510-2 as previously described with reference to FIG. 2 . Inaddition, the NSTR MLD 504 transmits a first PPDU 514-1 that includes afirst A-MPDU 516-1 with frames from a first AC (i.e., AC_BE (whosebackoff counter is zero) as the primary AC) on link1 502-1 at a firststart time 518-1 and a second PPDU 514-2 that includes a second A-MPDU516-2 with frames from a second AC (i.e., AC_BE (whose backoff counteris zero) as the primary AC) on link2 502-2 at a second start time 518-2after STA1 506-1 of the NSTR MLD 504 performs a first backoff operationon link1 502-1 that includes a first backoff counter 512-1 of the firstbackoff operation, and STA2 506-2 of the NSTR MLD 504 performs a secondbackoff operation on link2 502-2 that includes a first backoff counter512-2 a of the second backoff operation and includes a second backoffcounter 512-2 b of the second backoff operation, similar to thetechnique as previously described with reference to FIG. 4 .

However, as shown in FIG. 5 , the first backoff counter 512-2 a of thesecond backoff operation and the second backoff counter 512-2 b of thesecond backoff operation become zero at different times, such that thefirst backoff counter 512-2 a of the second backoff operation has avalue of four (shown by four slots included in the first backoff counter512-2 a on link2 502-2) and the second backoff counter 512-2 b of thesecond backoff operation has a value of six (shown by six slots includedin the second backoff counter 512-2 b on link2 502-2). In an embodiment,STA2 502-2 may perform another backoff operation because the second PPDU514-2 did not include frames from AC_VO, such that rules may need to bedefined for a CW[AC_VO] and a QSRC[AC_VO] when the backoff counters on alink (e.g., link2 502-2) end at different times.

In one embodiment, the NSTR MLD 504 may perform another backoffoperation (not shown) on link2 502-2 for an AC (e.g., AC1) whose frameswere not included in the second PPDU 514-2 and whose backoff counterbecame zero at a different time (shown) or at a same time (not shown)from another AC (e.g., AC2) whose frames were included in the secondPPDU 514-2, such that a QSRC[AC1] is increased by one and a CW[AC1] isdoubled if the CW[AC1] is less than a CWmax[AC1] for AC1, whose frameswere not included. In another embodiment, after transmission of thesecond PPDU 514-2, the NSTR MLD 504 may perform another backoffoperation (not shown) on link2 502-2 for AC1, whose frames were notincluded in the second PPDU 514-2, and whose backoff counter became zeroat a different time from AC2, whose frames were included in the secondPPDU 514-2, such that a CW[AC1] and a QSRC[AC1] are unchanged for AC1.

Similar backoff operations as previously described may also beimplemented by an NSTR MLD to break a deadlock on multiple links. Anexample of a deadlock that occurs on multiple links is described infurther detail with reference to FIG. 6 .

FIG. 6 illustrates an example of a deadlock that occurs on multiplelinks. In the embodiment of FIG. 6 , an NSTR MLD 604 includes STA1 606-1and STA2 606-2 and communicates via link1 602-1 and link2 602-2 with anMLD 608 that includes AP1 610-1 and AP2 610-2 as previously describedwith reference to FIG. 2 .

STA1 606-1 of the NSTR MLD 604 performs a first backoff operation onlink1 602-1 where a first backoff counter 612-1 of the first backoffoperation corresponds to a first AC (e.g., AC_BE) and has a value of ten(shown by ten slots included in the first backoff counter 612-1 on link1602-1). In addition, STA2 606-2 of the NSTR MLD 604 performs a secondbackoff operation on link2 602-2 where a first backoff counter 612-2 ofthe second backoff operation corresponds to a second AC (e.g., AC_VO)and has a value of two (shown by two slots included in the first backoffcounter 612-2 on link2 602-2).

In an embodiment, the first backoff counter 612-2 of the second backoffoperation becomes zero at a first time 618-1, such that link2 602-2starts waiting for the first backoff counter 612-1 of the first backoffoperation on link1 602-1 to become zero. At a second time 618-2, link2602-2 becomes busy and begins a busy period 614. During the busy period614 on link2 602-2, the first backoff counter 612-1 of the first backoffoperation on link1 602-1 becomes zero at a third time 618-3, at whichlink1 602-1 starts waiting for link2 602-2 to have a backoff counterbecome zero. At a fourth time 618-4, the busy period 614 ends and link2602-2 starts waiting for link1 602-1 to have a backoff counter becomezero. However, when link1 602-1 and link2 602-2 are both waiting forbackoff counters to become zero, a deadlock occurs. As an example,during “deadlock”, the two links, 602-1 and 602-2, may not be used forframe exchanges by STA1 606-1 and STA2 606-2 of the NSTR MLD 604.

To break the deadlock and allow frame exchanges, the NSTR MLD 604 mayimplement a technique as described herein. In one embodiment, breakingthe deadlock may involve another backoff operation being performed onlink2 602-2 once a backoff counter on link1 602-1 becomes zero. Inanother embodiment, breaking the deadlock may involve another backoffoperation being performed on link2 602-2 once link2 602-2 becomes idle.In such embodiment, after the deadlock is broken, the NSTR MLD 604 maytransmit PPDUs on link1 602-1 and/or link2 602-2.

FIG. 7 illustrates a flow diagram of a technique for multi-linkoperations in accordance with an embodiment of the invention. At block702, an NSTR MLD performs a first backoff operation on a first link anda second backoff operation on a second link. At block 704, the NSTR MLDtransmits a first PPDU on the first link at a first start time after thefirst backoff operation and a second PPDU on the second link at a secondstart time after the second backoff operation.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be implemented in anintermittent and/or alternating manner.

It should also be noted that at least some of the operations for themethods described herein may be implemented using software instructionsstored on a computer useable storage medium for execution by a computer.As an example, an embodiment of a computer program product includes acomputer useable storage medium to store a computer readable program.

The computer-useable or computer-readable storage medium can be anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system (or apparatus or device). Examples ofnon-transitory computer-useable and computer-readable storage mediainclude a semiconductor or solid-state memory, magnetic tape, aremovable computer diskette, a random-access memory (RAM), a read-onlymemory (ROM), a rigid magnetic disk, and an optical disk. Currentexamples of optical disks include a compact disk with read only memory(CD-ROM), a compact disk with read/write (CD-R/W), and a digital videodisk (DVD).

Alternatively, embodiments of the invention may be implemented entirelyin hardware or in an implementation containing both hardware andsoftware elements. In embodiments which use software, the software mayinclude but is not limited to firmware, resident software, microcode,etc.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The scope of theinvention is to be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A device comprising: a processor configured to:perform a first backoff operation on a first link and a second backoffoperation on a second link of a multi-link device (MLD) that has anon-simultaneous transmission and reception capability (NSTR MLD); andtransmit a first Physical Layer Convergence Protocol (PLCP) ProtocolData Unit (PPDU) on the first link at a first start time after the firstbackoff operation and a second PPDU on the second link at a second starttime after the second backoff operation.
 2. The device of claim 1,wherein a difference between the first start time and the second starttime is no more than a Receive-Transmit Turnaround Time(aRxTxTurnaroundTime).
 3. The device of claim 1, wherein a differencebetween the first start time and the second start time is no more than 4microseconds (p).
 4. The device of claim 1, wherein a first backoffcounter of the first backoff operation becomes zero after a firstbackoff counter of the second backoff operation and a second backoffcounter of the second backoff operation have become zero.
 5. The deviceof claim 4, wherein the first backoff counter of the second backoffoperation and the second backoff counter of the second backoff operationbecome zero at different times.
 6. The device of claim 4, wherein thefirst backoff counter of the second backoff operation and the secondbackoff counter of the second backoff operation become zero at a sametime.
 7. The device of claim 1, wherein the first PPDU includes a firstAggregated-Media Access Control (MAC) Protocol Data Unit (MPDU) (A-MPDU)with frames from a first Access Category (AC), and the second PPDUincludes a second A-MPDU with frames from a second AC.
 8. The device ofclaim 7, wherein the processor is configured to perform another backoffoperation on the second link for an AC that is not included in thesecond PPDU, and wherein a Contention Window (CW) of the AC (CW[AC]) anda Quality of Service (QoS) Short Reply Counter (QSRC) of the AC(QSRC[AC]) are unchanged.
 9. The device of claim 7, wherein theprocessor is configured to perform another backoff operation on thesecond link for an AC that is not included in the second PPDU after aQSRC[AC] is increased by one and a CW[AC] is doubled.
 10. The device ofclaim 9, wherein the CW[AC] is doubled if the CW[AC] is less than a maxCW of the AC (CWmax[AC]).
 11. The device of claim 9, wherein the CW[AC]is set to a minimum CW of the AC (CWmin[AC]) if the QSRC[AC] reaches athreshold value.
 12. The device of claim 1, wherein a first backoffcounter of the first backoff operation becomes zero after a firstbackoff counter of the second backoff operation and a second backoffcounter of the second backoff operation have become zero; and whereinthe first PPDU includes a first A-MPDU with frames from a first AC andthe second PPDU includes a second A-MPDU with frames from a second AC.13. The device of claim 12, wherein the second A-MPDU with frames fromthe second AC corresponds to at least one of the first backoff counterof the second backoff operation and the second backoff counter of thesecond backoff operation.
 14. The device of claim 1, wherein theprocessor is configured to perform another backoff operation on thesecond link once a backoff counter on the first link becomes zero tobreak a deadlock that occurs after the first backoff operation and thesecond backoff operation.
 15. The device of claim 1, wherein theprocessor is configured to perform another backoff operation on thesecond link once the second link becomes idle to break a deadlock thatoccurs after the first backoff operation and the second backoffoperation.
 16. The device of claim 1, wherein the first backoffoperation includes a backoff counter for a corresponding AC and thesecond backoff operation includes another backoff counter for anothercorresponding AC.
 17. The device of claim 1, wherein the deviceincludes: a first station (STA), STA1, that performs the first backoffoperation on the first link; and a second STA, STA2, that performs thesecond backoff operation on the second link.
 18. The device of claim 1,wherein the processor is configured to operate according to an Instituteof Electrical and Electronics Engineers (IEEE) 802.11be communicationprotocol.
 19. A method of multi-link operations, the method comprising:performing, by a multi-link device (MLD) that has a non-simultaneoustransmission and reception capability (NSTR MLD), a first backoffoperation on a first link and a second backoff operation on a secondlink; and transmitting, by the NSTR MLD, a first Physical LayerConvergence Protocol (PLCP) Protocol Data Unit (PPDU) on the first linkat a first start time after the first backoff operation and a secondPPDU on the second link at a second start time after the second backoffoperation.
 20. A method of multi-link operations, the method comprising:performing, by a multi-link device (MLD) that has a non-simultaneoustransmission and reception capability (NSTR MLD), a first backoffoperation on a first link and a second backoff operation on a secondlink, wherein performing the first backoff operation and the secondbackoff operation includes: a first station (STA), STA1, performing thefirst backoff operation on the first link; and a second STA, STA2,performing the second backoff operation on the second link; andtransmitting, by STA1 and STA2, a first Physical Layer ConvergenceProtocol (PLCP) Protocol Data Unit (PPDU) on the first link at a firststart time after the first backoff operation and a second PPDU on thesecond link at a second start time after the second backoff operation.